Main idea: Fusion x100 and fun realm, so no need for cross realm.
How?
-Making the choice when u create a new character between leveling with x100 rates or going instant lvl90.
-Making PvE content work properly in this fusion realm.
-About PvE npc's: make each pve item cost 15k conquest so it won't be ez to get all the pve stuff and people will try to farm it doing PvE dungeons from pandaria.
(PvE should be doable for this)
With fusion, no cross, no problems with lag or bugs, bigger players comunity
Also could consider a Cross faction bg's for faster que's, like you can que bg but u won't know if u will be horde or aliance, just like how it works for 10c10 (in rated bg's 2 aliance teams can fight each other, and 1 of the teams play as horde) so more que's will call.
For example, 60 aliance in que? no problem 3 bg's of 10c10 teams, all aliance players but some of them playing as hordes like in 10c10.
50 aliance and 10 hordes? some hordes can play with the aliance faction and some aliance with the horde faction, just think about how it works for 10c10 rated.
-Make a IP ban system for people that got banned appearing in reports with proffs(videos) of them hacking by Teleport hack or Fly hack, so they can't do new accounts again and again.
-Get more info about hacks/bots like WPE or PQR, visit hacker forums time to time to see what's going on and prevent hacks/bugs to occur in your server.